Haengjusanseong, Korean fortress in Haengju-dong, South Korea.

Haengjusanseong is a fortress with stone walls and watchtowers positioned strategically above the Han River. The structure spreads across multiple sections that together formed a connected defensive system, and visitors can walk along the preserved remains today.

Haengjusanseong is a mountain fortress on Mount Deogyang, built as an earthen rampart along the 7th–8th ridge lines, with a circumference of about 1 km. It was the site of the 1593 Battle of Haengju, where General Kwon Yul defeated Japanese forces during the Imjin War. The fortress was designated Historic Site No. 56 on January 21, 1963.

The summit holds a 1603 memorial stele for the victory, while the present monument dates from 1963; a reconstruction stele from 1845 stands before Haengju Seowon. The fortress grounds host the Haengju Sunrise Festival, the Goyang Haengju Cultural Festival and the Haengju Street Arts Night.

Visitors follow marked paths along the walls and can view the surrounding landscape and river from various points. Information panels at different locations explain how the various parts of the fortification worked and protected the area.

The fortress is a twin-walled structure: a small inner wall rings the summit, while an outer wall encloses a valley to the north. The 1603 Haengju Great Victory Monument stands on the summit; the present memorial there was erected in 1963.